I appear to have encountered a bug which keeps me from finishing my class (Imperial Agent) quest. I've kept this as spoiler-free as possible. At the end of of Doom and the Dark Temple quest, there is a potential additional battle. It was difficult enough that, after a few tries, I walked out of the instance rather than give it another go. I have since been locked out of the instance, it indicating that I am "not eligible to enter at this time." But because I haven't finished this final battle, I can't continue on the class quest.